As methods of forming a thin-film inorganic layer, the use of inorganic particles has been proposed. For example, an inorganic thin film having high compactness may be formed in a manner in which inorganic particles are dispersed in a binder and a solvent and the resulting solution is applied using any coating process to form a thin film, which is then fired at a high temperature to remove the binder. When a thin film is manufactured in this way, the compactness of the inorganic thin film is determined based on the extent of dispersion of inorganic particles and the amount of binder. Furthermore, the firing temperature may be adjusted depending on the size of the primary inorganic particles. For example, the use of nano-sized inorganic particles enables the firing temperature to be lowered.
This method may be utilized in the field of a solid oxide fuel cell (SOFC).
A fuel cell is a device for directly converting the chemical energy of fuel into electrical energy through an electrochemical reaction, and is advantageous because it has high energy conversion efficiency compared to typical heat engines, thus reducing fuel consumption and greenhouse gas emissions. A fuel cell, especially a solid oxide fuel cell, uses an inorganic electrolyte membrane having high ion conductivity at high temperatures. As research and development into SOFCs has been carried out all over the world, the most advanced form currently has reached the practical testing phase of a 100 kW power generation system, and other kinds of SOFC are under systematic development. However, an inorganic electrolyte for an SOFC has high ion conductivity at high operating temperatures (800 to 1,000° C.), thus making it difficult to manufacture and maintain a fuel cell stack. Hence, in order to reduce the costs of manufacturing and operating fuel cells, there is a need to develop an electrolyte material having high ion conductivity at intermediate or low operating temperatures (600 to 800° C.). Since a ceria (CeO2) material has relatively high ion conductivity compared to a zirconia (ZrO2) electrolyte, which is conventionally used for SOFCs, thorough research thereto is ongoing as an alternative to a solid electrolyte for SOFCs at intermediate or low temperatures. Furthermore, compared to conventional yttria (Y2O3) materials, ceria exhibits high ion conductivity, and thus the operating temperature may be decreased, whereby a longer stack lifetime, selection from among a broader range of materials necessary for the entire system, and the generation of many economic benefits are anticipated.